Some conventional antenna devices utilize a dipole antenna, (for example, as in Patent Literature 1). In addition to the self-supporting type antenna devices like the antenna device disclosed in Patent Literature 1, there are also antenna devices that support an antenna element by a guy wire, (for example, as in Patent Literature 2). The antenna device disclosed in Patent Literature 2 utilizes a monopole antenna.
In general, in order to construct a high-gain dipole antenna, an antenna length that is substantially equivalent to a half wavelength of the utilized radio wave is necessary. Conversely, in order to construct a monopole antenna, an antenna length that is substantially equivalent to a quarter wavelength is necessary. When the frequency of the utilized radio wave is low, the antenna becomes several meters long. Hence, the assembly (installation) of an antenna device and the installation of the parts are quite cumbersome. In addition, the securing of wind resistance and earthquake resistance for an extremely long antenna element, as disclosed in Patent Literature 2, requires the fastening of the antenna element to a base using support members such as a large number of guy wires.
In order to avoid increase in installation area required for an antenna device and increase of parts cost and device maintenance cost, a high-gain and compact antenna is desired that does not need a large number of support members. In general, scheme for bending an exciter part is known as a scheme for suppressing gain reduction and for downsizing a linear antenna (for example, see Patent Literature 3 and Patent Literature 4). According to this scheme, downsizing and the securing of the necessary electrical length of the exciter part to maintain the gain can be simultaneously accomplished.